The present invention pertains to a device with a gas sensor for measuring a breathing gas component in a breathing gas line, which is connected via a breathing gas delivery device to a gas supply line for breathing gas and with a bypass line extending from the breathing gas line to the gas supply line.
A respirator with a delivery device for breathing gas, which draws in ambient air and pumps it into a breathing gas line leading to a patient, has become known from DE 197 08 094 A1. By returning part of the breathing gas drawn in into the area of the intake side of the delivery device and simultaneously introducing oxygen from an oxygen source into the gas supply line, the oxygen concentration in the breathing gas can be adapted to the patient""s needs. The oxygen concentration in the breathing gas is measured with an oxygen sensor in the breathing gas line. In addition to the oxygen concentration, the breathing gas flow and the respiration pressure are determined as well.
Pressure variations occur in the breathing gas line due to the interplay of inspiration and expiration, and they affect the accuracy of the oxygen concentration measurement. Even though it would be possible to calculate correction values for the oxygen concentration by the pressure measurement, which is performed in the vicinity of the oxygen sensor, complicated evaluating logarithms are needed for this, because both the course of the pressure over time and the course of the oxygen concentration over time must be evaluated simultaneously. Correspondingly corrected measured values for the oxygen concentration are therefore available only after a certain time and therefore they also contain a high inaccuracy. If the oxygen sensor is used in the control circuit as an actual value transducer for the oxygen concentration to be set, delays and inaccuracies in the determination of the actual value are not acceptable, because these would compromise the control.
The primary object of the present invention is to improve a respirator of the type described such that a pressure correction of the oxygen concentration measurement can be performed without appreciably affecting of the respiration pressure.
According to the invention, a device is provided with a gas sensor for measuring a breathing gas component in a breathing gas line. The breathing gas line is connected via a breathing gas delivery device to a gas supply line for breathing gas and with a bypass line extending from the breathing gas line to the gas supply line. A first measuring gas line with a first electrochemical measuring cell as a gas sensor is provided in parallel to the bypass line. A first throttling point is provided in the course of the first measuring gas line between the first electrochemical measuring cell and the breathing gas line. A first pressure sensor is located downstream of the first electrochemical measuring cell. A junction point for the first measuring gas line is arranged within the gas supply line upstream of the bypass line.
The advantage of the present invention is essentially that by arranging the oxygen sensor in a measuring gas line leading from the breathing gas line to the gas supply line in the intake area of the breathing gas delivery device and by arranging a throttling point upstream of the first electrochemical measuring cell, a measurement of the oxygen concentration is carried out in the so-called bypass flow without pressure variations in the breathing gas line appreciably affecting the gas flow in the area of the first electrochemical measuring cell. A measuring gas flow, which flows off via the first electrochemical measuring cell into the gas supply line, is branched off from the breathing gas line through the first throttling point. In terms of pressure, the gas supply line is somewhat below the ambient pressure level. The pressure downstream of the first throttling point is determined with a first pressure sensor, which records only slight pressure variations compared with the pressure measurement in the breathing gas line, to which the respiratory pressure is admitted.
The measuring gas flow over the first electrochemical measuring cell is on the order of magnitude of about 200 mL per minute. By returning the measuring gas into the gas supply line, no breathing gas is lost from the breathing gas line.
A second measuring gas line, with a second electrochemical measuring cell, may advantageously be arranged in parallel to the first measuring gas line. The second electrochemical measuring cell is used to monitor the first electrochemical measuring cell, on the one hand, and, on the other hand, it is used as an actual value transducer for the oxygen concentration in case the first electrochemical measuring cell is not active or is in the calibration mode. A second throttling point, with which the second electrochemical measuring cell is uncoupled from the pressure prevailing in the breathing gas line, is arranged between the breathing gas line and the second electrochemical measuring cell within the second measuring gas line.
The branch-off point for the measuring gas line may advantageously be arranged within the breathing gas line before the branch-off point of the bypass line in the direction of flow. It is thus achieved that a pressure, which is higher than the ambient pressure level and ensures the measuring gas flow through the measuring gas lines, is always present at the branch-off point.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawing and descriptive matter in which a preferred embodiment of the invention is illustrated.